To meet a variety of advanced aircraft and aerospace requirements, there is a need for high temperature thermoset resins for matrix and adhesive applications. Such resins, because of the complexity of structure, the high glass transition temperature needed and high temperature thermooxidative stability required, have critical processing difficulties when required to conform to the state-of-the-art processing criteria. OSHA requirements negate processing such materials from solvent base systems, thereby necessitating fabrication of the resins via melt techniques.
As disclosed in U.S. Pat. Nos. 3,966,729 and 4,147,868, recent advances in matrix and adhesive resins have resulted in the discovery of new phenylquinoxaline resins terminated by primary acetylene groups. The acetylene moiety can be thermally homopolymerized between 200.degree. and 250.degree. C. to form a moisture insensitive, high temperature resin system. Although the materials show excellent resistance to heat and environmental surroundings, they lack the necessary flow required for melt processing because of their high glass transition temperature (Tg) (140.degree.-170.degree. C.).
It is a principal object of this invention, therefore, to reduce the Tg of selected acetylene-terminated phenylquinoxaline oligomers so that they have flow characteristics required for melt processing.
Another object of the invention is to provide a composition containing an acetylene-terminated phenylquinoxaline oligomer and, as a reactive diluent, an acetylene-substituted aromatic ether.
A further object of the invention is to provide oligomer-reactive diluent materials which co-cure on thermal treatment.
Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the ensuing disclosure and the drawing which shows graphically the cure rheometry, i.e., variations in viscosity with time at certain constant temperatures, of compositions of this invention and of oligomers per se.